Electrical measuring instrument



May 14, 1946. A. WOLF 2,400,325

ELEcTRicAn umsunine Ins'rmnmm Filed Sept. so, 1943 I r I I"? INVENTOR WWay;

m e! I A ORNEYS ins. wherein the single flsu is'a STATE rinsc'mroar.smasunmd nvs'rarnmn'r Alfred Wolf, Tulsa, Okla., assignor toGeophysical- Corporation, New York,

poration of New' Jersc! Application September so, 1943, Serial No.504,391 4 Claims. (01. ru -95 This invention relatesto electricalmeasuring instruments. V. 7

An object of this invention is an instrument for measuring the ratio oftwo alternating current voltages of the same frequency.

In general, the measuring instrument comprises a vacuum tube amplifierof the automatic volume control type in conjunction with a frequencychanger. The output voltage of the amplifier is impressed upon twofilters, the first of which is tuned'topass only one, frequency and theother of which is tuned to pass only afrequency other than said onefrequency., The first filteris connected to a voltage responsiveregisteringinstrument while the second filter, through suitablerectifying means, supplies-direct current voltage a second arm containsavacuum tube-rectifier i8 and a battery I9 and the two remaining armsrespectively contain the resistors 20 and II. The

direction of permissible current flow through the rectifier i8 is fromthe terminal "to terminal i2 .while the direction of permissible currentfiow through the rectifier I 8 is from the terminal I! to the terminalIt. The two rectifiers liand ll for controlling the attenuator elementof the amplifier. The frequency changer has its output connected to theinput oi! the amplifier. The

alternating current voltages of the-same given frequency are fed one tothe amplifier input and.

the other to the frequency changer outputandthe first filter is tuned topass only said given frequency. The frequency changer changes the secondvoltage to the frequency passed by the second filter so that one voltageis impressed on the amplifier at the frequency passed by the firstfilter and the other voltage .is impressed on the amplifier at thefrequency-passed by thesecond filter. The attenuator element of theamplifier is controlled'only by rectified voltage of thefrequencypassedbythesecondniterwiththeresult that-the amount ofattenuation. efiectedby the attenuator is proportional to the impressedalternating current voltage of that frequency. The voltage reaching there proportional to the impressed voltage of the freinstrument is quencypassed by the firstfilter andis attenuated by an amount to the impres dvoltage of the. frequency passed by the secondfilter with the resultthat the register indicates theratiobetweenthetwovoltasec- Otherobjects, novel features and advantages I ofthis invention will becomeapporentfroin the following specification and drawcircuit diagram ofanembodiment of-the invention. 1

In thedrawing, ll designates'a transformer having primary terminals mand lglb,the secondary of which feeds into-an attenuator. con

together with the resistors II and 2| constitute a variable resistancewhich is a function of direct current voltage applied to'the terminalsI4 and i I. The direct current voltage for controlling the valueoftheresi'stanceiust referredto is degenerative direct current voltageobtained from a, 7 source later to be described. The voltage of thebatteries l1 and I! is usually made sufiiciently. great that no currentfiows through the rectifiers when thedirect current voltage appled-between the terminals it and Ii is zero. Under these circumstances,the alternating current voltage drop,

across the circuit W has the same amplitude as the alternating currentvoltage induced in the secondary of the transformer ll. [Uponapplication of direct current voltage between-the terminals H and I! insucha direction as to overcome the polarized voltages of the batteriesi1 and "and make the rectifier; II and i8 conductive, the 'altem'atingcurrent voltage drop across the circuit W becomes smaller than thealternating current voltage induced in the secondary of the transformerI. The value of the;

attenuation'thus obtained isthe ratio of the resistance W to-the sum ofthe resistances ii and W. By making the resistance 1 I sufficientlygreat the attenuation ratio can be made very large.

The voltage drop across the clrcuitiW is impressed between the controlelectrode 22 and the v cathode II of a vacuum tube amplifier It. The

anode II of the amplifier is connected to the cathode through a battery26 and a resistance 21.

- the filter 20 is tuned to pass another frequency as different fromsaid one frequency. The outputof the filter-ll is fed to a-iyoltageresponsive registering instrument such, for example, as a recorder It;

sisting of a resistance Ii injuries with a Wheairstone bridge circuit whaving terminals", ls. u

andil. OnearmofthecircuitWcontainsavacmantuberectifierilandabatteryllwhilele The aims of the-filter a isfedto the primary of a 3|;the secondary of which constitutes Port of,the input circuit of a full wave rectifier 3L Theoutput of the rectifierI2 is fed througharesistance condenser network fltothe terminals and iiofthe circuitw.- Atransformerllhavingprlmaryterminalsflaandflb'lhe'voltage drop acrossthe resistance fl'is impressed upon a filter Itand upon a filterjl. The -filter2listunedtopassonlyone frequencywhilehalite- "aoondary forming of a circuit 8| which constitutes a balancedmodulator employed as a frequency changer as described by R. S.Caruthers, Bell System Technical Journal, volume 18, April 1939. Carrierfrequency is supplied to the modulator at the terminals 36. The outputof the circuit 35 is fed through a transformer 31 and switch 38 to'theprimary of a transformer ll, the secondary of which is connected inseries with the secondary of the transformer III.

In the operation of the above-described circuit to measure the ratio oftwo voltages E1 and E: of the same frequency 1, voltage E1 is impressedupon the primary of the transformer II and voltage E: is impressed uponthe primary of the transformer fl. The voltage E1 at frequency 11 is feddirectly into the attenuator. The voltage E2 is changed from frequency hto frequency I: by the balanced modulator 35 through the action of thecarrier frequency voltage supplied to the terminals 36. The voltage E:at frequency In is then fed into the attenuator. The filter 28 is tunedto pass frequency f1 and reject frequency 3'! from the transformer 30and connect the frequency doubler 40 to the transformer 38 instead.

It is 'of course understood that other modifications may be made in thedevice above described without in any way departing from the'spirit ofthe invention as defined in the appended claims. 7 I claim: v

1. A device for measuring the ratio of two alternating current voltagesof the same given frequency comprising an alternating'current voltageattenuator controlled by impressing direct current voltage thereon, afrequencychanger having its output connected to the inputof saidattenuator, a vacuum tube amplifier having its input connected to theoutput of said attenuator, a

first filter connected to said amplifier output and capable of passingsaid given frequency only, a

register connected to said first filter, asecond filter connected to theamplifier output and capable of passing said frequency changer outputwhile rejecting said given frequency, means for rectifying the output ofsaid second filter and impressing the rectified output on saidattenuator ing current voltage supplied thereto, means for' impressingone of said voltages on the input of said attenuator and means forimpressing the other of said voltages on the input of said fretween theterminals it and I5 controls the frequency j: voltage between the gridand cathode of the amplifier 24 in such manner that a change in thevoltage impressed on the transformer 30 produces no change in the hfrequency output voltage of the amplifier. The circuit consisting of theattenuator, amplifier, filter 29 and rectifier 32 constitute in effectan automatic volume. control amplifier for voltages of frequency is. The

attenuation effect on the I: frequency voltage is therefore proportionalto the E: voltage impressed on the transformer 39. Consequently. theattenuation effected by the attenuator on the operated to disconnect thebalanced modulator quency changer.

2. A device for measuring the ratio of two alternating current voltagesof the same given frequency comprising an alternating current voltageattenuator controlled by impressing direct current voltage thereon, afrequency changer having its output connected to the input of saidattenuator, a vacuum tube amplifier having its input connected to theoutput of said attenuator, a

first filter connected to said amplifier output and output and capableof passing said frequency voltage impressed on the transformer. isipr'ochanger joutput while rejecting said given frequency, means forrectifying the output of said second filter and impressing the rectifiedoutput on said attenuator to control its attenuating effeet on thealternating current voltage supplied thereto, means for impressing oneof said voltages on the input of said attenuator and means forimpressing the other of said voltages on the input of said frequencychanger.

3. A deviceaccording to claim 1 in-which said attenuator is of thevariable impedance type.

4. A device according to claim 2 in which said attenuator is of thevariable impedance type.

AIJ'RED WOLF.

